The present invention relates to a center-foldable seat back, a seat provided with the center-foldable seat back, and a method of manufacturing the center-foldable seat back. More particularly, it relates to a center-foldable seat back in which a seat back upper part of the seat back can be tilted forward relative to a seat back lower part, a vehicle seat provided with the center-foldable seat back, and a method of manufacturing the center-foldable seat back.
A center-foldable seat back is a design with an associated technique enabling a seat back upper part to tilt forward relative to a seat back lower part, and various types of designs and associated techniques for the center-foldable seat back have conventionally been proposed.
Since the center-foldable seat back is configured so that the seat back upper part can be tilted forward relative to the seat back lower part, various designs have been made in covering the seat back upper part and the seat back lower part with a trim cover.
For example, as the trim cover, a technique has been known in which the seat back upper part is covered with an upper cover, the seat back lower part is covered with a lower cover, and the upper cover and the lower cover are sewn together along the entire periphery so that no gap is provided between the seat back upper part and the seat back lower part. According to this technique, the seat back can be configured so that the internal structure of the seat back is not exposed to the outside due to the trim cover, and no gap is provided between the seat back upper part and the seat back lower part.
For the center-foldable seat back provided with the trim cover in which the upper cover and the lower cover are sewn together along the entire periphery, a technique has been proposed in which the trim cover is provided with a tension cloth by being extended inward from the upper cover and the lower cover of the trim cover to modulate the pulled-in state and to prevent wrinkles from occurring on the seat surface side of trim cover when the upper frame tilts.
For example, a technique has been proposed in which a plurality of tension cloths folded double in a bag shape are sewn together to the peripheral ends of the upper cover and the lower cover of the trim cover with an appropriate space being provided therebetween, an extensible member such as a rubber string is inserted through the tension cloths, and the ends of the extensible member are fixed to each other by a hook ring, as can be seen in Japanese Unexamined Patent Application Publication No. 2001-180343 (“the '343 Publication”) (see paragraph 0024, FIG. 4).
Another technique has been proposed in which a tension cloth in the front and rear direction is provided to extend inward from the ends of a central portion excluding the right and left portions on the inside of the trim cover as side frame insertion parts, the rear side edge and the front side edge of tension cloth are fixed to each other by a hook ring, and a wire supporting the tension cloth is provided to project downward from an upper frame so that the pressing force can be changed in an erected state or a tilted state of the upper frame, as is seen in Japanese Unexamined Patent Application Publication No. 2001-197956 (“the '956 Publication”).
As still another proposed technique, a technique has also been proposed in which a band-like rubber string provided with a resin hook at the front side edge thereof is provided in the back-side central portion, a tension cloth is provided in the front-side central portion, the rubber string is locked to a wire projecting downward from an upper frame by the resin hook to pull the back-side central portion, and the front-side tension cloth is fixed to a back-side joint flap and is pulled, as is seen in Japanese Unexamined Patent Application Publication No. 2001-199266 (“the '266 Publication”).
For the above-described center-foldable seat back, it is anticipated that the pulled-in state is modulated by the tension cloth, and wrinkles are prevented from occurring on the seat surface side of the trim cover.
All of the above-described proposed techniques have a disadvantage that the construction is complicated, so that much time and labor are required for putting the trim cover including the assembling of tension cloth and other members, thereby lowering the work efficiency. That is, in addition to the work for putting the trim cover, the hook ring and the like must be installed in a covered state, so that it is necessary to perform work in a very tight space, which presents a disadvantage that not only the worker requires high skill but also the work efficiency is low.
Also, in the above-described proposed techniques, the trim cover must be put between the upper frame and the lower frame, and further work for applying tension to the tension cloth by another member must be performed. Therefore, improvement has not been made on a point on which the trim cover is put considering the upper frame and the lower frame.